Fuel is introduced into the cylinders of an internal combustion engine and combusted. The combustion of fuel releases energy which is converted into mechanical movement by means of the piston. Usually the operation of a cylinder is divided into four strokes: intake of fuel, compression stroke, expansion stroke and exhaust removal. The combustion of fuel takes place between the compression and expansion strokes. Together the strokes form a cylinder cycle in which the piston of the cylinder has moved according to the strokes and returned to the initial position. The work done during the stroke is transmitted to the crankshaft. In order to have as smooth a rotation of the crankshaft it is preferable to have each cylinder produce a similar amount of work during the cycle. This is the aim of balancing the cylinders.
It is known to use measuring the temperature of the engine exhaust gas for balancing the cylinders, especially at low engine loads. (is it measured for each cylinder) The amount of fuel introduced into each cylinder is adjusted on the basis of the measurements. The amount of fuel has an effect on the amount of work the cylinder produces. This method, however, includes a certain delay.
When the engine load is higher, engine knock must be taken into account, as knocking can damage the engine. The reason for engine knock is spontaneous ignition of the fuel in the cylinder, causing an undesired method and timing of combustion. Engine knock is often divided into light knock and heavy knock. Light knock describes low fluctuations in the cylinder pressure. Heavy knock describes the highest fluctuations in the cylinder pressure. Light knock is reduced by controlling the ignition timing or the fuel/air ratio. Heavy knock is reduced by reducing the engine load (reducing the amount of fuel) or by even shutting the engine down, if other means are not enough. Knocking is cylinder-specific, so knock adjustment is cylinder-specific as well. Cylinder-specific knock sensors are used for detecting the level of knock. Thus, on highest engine loads the balancing of cylinders is carried out by means of adjustment for light knock. If the engine does not knock, the cylinders are not balanced. Thus, the problems of prior art are that there is a delay in balancing the cylinders and the balancing is necessarily made when the engine is running at highest loads.